This invention relates to bar code scanners ("readers") and, in particular, to a bar code scanner suitable for use with a variety of different host terminals having different operating characteristics, with the scanner being operable at different frequencies for reducing power consumption.
Bar code scanners are designed to read (sense or scan) bar code data and to convert the sensed data into a form suitable for use with a host terminal. Host terminals may be any one of a large group of machines, such as the IBM 4683, any IBM PC, DEC terminals, or the TELXON 710, among others. These machines have different operating characteristics. It is desirable to have a bar code scanner which can be operated and be compatible with a large number of these different type of host terminals.
A bar code scanner may be powered via a battery pack integral to the scanner or it may be powered from a host terminal to which it is connected via a wire or cable. The host terminal in turn may be of the type which is line powered (e.g., 110 v, 60 Hz) or it may be of the type which is battery powered. When the bar code scanner is connected to a line powered host terminal, the power consumption of the scanner is normally not critical and is not of concern to the user or operator of the bar code scanner. However, when the bar code scanner derives its power from a battery operated host terminal or when the scanner is powered by its own battery pack the power dissipation (consumption) of the scanner becomes critical. It is elementary that it is desirable and/or necessary to reduce the amount of power used by a battery operated system whereby it can be used for a longer period of time without the need to either recharge the battery or replace it.
The host terminals normally dictate the speed at which they will accept or supply data and they impose their requirements on the bar code scanners with which they interface. As noted above, line powered host terminals are, typically, not designed with the aim of conserving power and will require that the bar code scanners to which they are connected be capable of operating at high speeds which normally results in a high degree of power consumption. On the other hand, battery operated host terminals are designed to conserve power and normally require that the bar code scanners with which they interface be capable of operating at lower speeds with a premium being placed on reducing power consumption.
A problem arises when it is desired to have a particular bar code scanner operate with different host terminals whose specifications and requirements are significantly different. For example, a scanner operable with an IBM point of sale (POS) terminal 4683, which functions as a cash register, must be capable of operating at high data rates. To operate at the high data rates the scanner must include a high speed microcontroller or microprocessor, capable of operating at high frequencies (e.g., 12 to 18 MHz). High speed microcontrollers are available but they and their associated circuitry and the resulting system tend to conduct relatively large currents and hence tend to dissipate a significant amount of power. However, the IBM 4683 host terminal is line powered and the power consumption of the system is of little, if any, concern.
The problem occurs when a scanner designed for use with a host terminal such as the IBM 4683 is also intended to be used with a battery operated host terminal whose speed and power requirements are much lower than those of the IBM 4683 and where it is important to conserve power. It is known to render the scanner with its high speed microcontroller compatible with the slow battery operated system by providing circuitry and/or software means within the microcontroller which can accept and handle high speed information and convert it for lower speed operation. This can be done, for example, by looping the information around shift registers (or by other known mechanisms) so as to render the data supplied by the microcontroller compatible with the data requirements of a slower battery operated host system.
However, this solution does not reduce the significant amount of power dissipated by the microcontroller itself which is being operated at the high speeds required for operation with the much faster host terminals such as the IBM 4683.